1. Field of the Invention
The present invention relates to gas delivery systems, such as, without limitation, PAP therapy systems for treating sleep apnea, ventilators, oxygen delivery systems, or other respiratory devices, and more particularly to methods of sanitizing the gas flow path within such gas delivery systems.
2. Description of the Related Art
Many individuals suffer from disordered breathing during sleep. Sleep apnea is a common example of such sleep disordered breathing suffered by millions of people throughout the world. One type of sleep apnea is obstructive sleep apnea (OSA), which is a condition in which sleep is repeatedly interrupted by an inability to breathe due to an obstruction of the airway; typically the upper airway or pharyngeal area. Obstruction of the airway is generally believed to be due, at least in part, to a general relaxation of the muscles which stabilize the upper airway segment, thereby allowing the tissues to collapse the airway. Another type of sleep apnea syndrome is a central apnea, which is a cessation of respiration due to the absence of respiratory signals from the brain's respiratory center. An apnea condition, whether OSA, central, or mixed, which is a combination of OSA and central, is defined as the complete or near cessation of breathing, for example a 90% or greater reduction in peak respiratory air-flow.
Those afflicted with sleep apnea experience sleep fragmentation and complete or nearly complete cessation of ventilation intermittently during sleep with potentially severe degrees of oxyhemoglobin desaturation. These symptoms may be translated clinically into extreme daytime sleepiness, cardiac arrhythmias, pulmonary-artery hypertension, congestive heart failure and/or cognitive dysfunction. Other consequences of sleep apnea include right ventricular dysfunction, carbon dioxide retention during wakefulness, as well as during sleep, and continuous reduced arterial oxygen tension. Sleep apnea sufferers may be at risk for excessive mortality from these factors as well as by an elevated risk for accidents while driving and/or operating potentially dangerous equipment.
Even if a patient does not suffer from a complete or nearly complete obstruction of the airway, it is also known that adverse effects, such as arousals from sleep, can occur where there is only a partial obstruction of the airway. Partial obstruction of the airway typically results in shallow breathing referred to as a hypoapnea. A hypopnea is typically defined as a 50% or greater reduction in the peak respiratory air-flow. Other types of sleep disordered breathing include, without limitation, upper airway resistance syndrome (UARS) and vibration of the airway, such as vibration of the pharyngeal wall, commonly referred to as snoring. Thus, in diagnosing a patient with a breathing disorder, such as OSA, central apneas, or UARS, it is important to detect accurately the occurrence of apneas and hypoapneas of the patient.
It is well known to treat sleep disordered breathing by applying a positive air pressure (PAP) to the patient's airway. This positive pressure effectively “splints” the airway, thereby maintaining an open passage to the lungs. In one type of PAP therapy, known as continuous positive air pressure (CPAP), the pressure of gas delivered to the patient is constant throughout the patient's breathing cycle. It is also known to provide a positive pressure therapy in which the pressure of gas delivered to the patient varies with the patient's breathing cycle, or varies with the patient's effort, to increase the comfort to the patient. This pressure support technique is referred to as bi-level pressure support, in which the inspiratory positive airway pressure (IPAP) delivered to the patient is higher than the expiratory positive airway pressure (EPAP).
In known gas delivery systems, an unclean gas flow path can lead to organisms, such as bacteria, viruses, fungi, or mold, being inhaled by the patient. These organisms, which usually grow in warm and moist locations, can cause harm to the patient. This often occurs when the same gas delivery system is used by multiple patients, such as in the PAP therapy system rental market, where the risk for the spread of disease is increased. One known method is to use a bacterial filter at the outlet of the device to prevent the backflow of bacteria from a patient into the PAP device. Another known method which addresses this problem involves using steam autoclaves or other gas sterilization devices to sterilize the gas flow path of a gas delivery system. However, the use of such devices is not cost efficient, and can also damage sensitive components within the gas delivery system. A further known method of sterilizing the gas flow path of a gas delivery system involves using cleaning agents, such as a cold sterilant, vinegar, alcohol, or soap and water, to clean the gas delivery system. However, such agents can likewise damage sensitive components of gas delivery systems and can also leave harmful residue that can be inhaled by the patient.
Furthermore, the problems just described are not limited to gas delivery systems in the form of PAP therapy systems for treating sleep apnea. Rather, such problems exist in connection with any type of gas delivery system used to deliver a flow of breathing gas to a patient, such as, without limitation, ventilators, oxygen delivery systems, or other respiratory devices.
There is thus room for improvement in field gas delivery systems, and in particular to the methods used to sterilize such gas delivery systems.